Metallocene catalyst systems

ABSTRACT

A catalyst system for polymerization of olefins having increased molecular weight and melting point is disclosed. A chiral, stereorigid metallocene compound having a silicon hydrocarbyl compound as an interannular bridge between two cyclopentadienyl or substituted cyclopentadienyl rings described by the formula (C 5  R&#39; m ) wherein R&#39; is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, each R&#39; being the same or different, is combined with an organoaluminum compound. The cyclopentadienyl ligands are coordinated with a metal of a group 4b, 5b, or 6b metal as designated in the Periodic Table of Elements. The metal is also bonded to a hydrocarbon radical or a halogen.

This is a continuation of application Ser. No. 07/317,089 filed on Feb.28, 1989, now abandoned, which is a continuation of application Ser. No.07/256,163 filed Oct. 7, 1988, now abandoned, which is a continuation ofapplication Ser. No. 07/034,472, filed Apr. 3, 1987, now abandoned.

TECHNICAL FIELD

The present invention provides a method for varying the melting pointsand molecular weights of polyolefins in a process of polymerizationusing metallocene catalysts. The catalysts used in the present inventionare chiral and stereorigid and include a bridge between thecyclopentadienyl groups. It has been discovered that changing thestructure and composition of the bridge leads to changes in the meltingpoints and molecular weights of the polymer products. It has also beendiscovered that addition of substituents to the cyclopentadienyl ringsalso influence these polymer properties. The present invention alsoincludes the ability to control the melting points of polyolefins,particularly polypropylene, by controlling the number of inversions inthe xylene insoluble fraction of the polymer chain.

BACKGROUND OF THE INVENTION

The present invention relates to the use of metallocene catalysts in theproduction of polyolefins, particularly polypropylene, and the abilityto vary certain properties of the polymer products by varying thestructure of the catalyst. In particular, it has been discovered thatchanges in the structure and composition of a bridge linking twocyclopentadienyl groups in the metallocene catalyst changes the meltingpoints and the molecular weights of the polymer products.

The use of metallocenes as catalysts for the polymerization of ethyleneis known in the art. German patent application 2,608,863 discloses acatalyst system for the polymerization of ethylene consisting ofbis(cyclopentadienyl)-titanium dialkyl, an aluminum trialkyl and water.German patent application 2,608,933 discloses an ethylene polymerizationcatalyst system consisting of zirconium metallocenes of the generalformula (cyclopentadienyl)_(n) Zr Y_(4-n), wherein Y represents R₁ CH₂AlR₂, CH₂ CH₂ AlR₂ and CH₂ CH (AlR₂)₂ wherein R stands for an alkyl ormetallo alkyl, and n is used a number within the range 1-4; and themetallocene catalyst is in combination with an aluminum trialkylcocatalyst and water.

The use of metallocenes as a catalyst in the copolymerization ofethylene and other alpha-olefins is also known in the art. U.S. Pat. No.4,542,199 to Kaminsky, et al. discloses a process for the polymerizationof olefins and particularly for the preparation of polyethylene andcopolymers of polyethylene and other alpha-olefins. The disclosedcatalyst system includes a catalyst of the formula (cyclopentadienyl)₂MeRHal in which R is a halogen, a cyclopentadienyl or a C₁ -C₆ alkylradical, Me is a transition metal, in particular zirconium, and Hal is ahalogen, in particular chlorine. The catalyst system also includes analuminoxane having the general formula Al₂ OR₄ (Al(R)-O)_(n) for alinear molecule and/or (Al(R)--O)_(n+2) for a cyclic molecule in which nis a number from 4-20 and R is a methyl or ethyl radical. A similarcatalyst system is disclosed in U.S. Pat. No. 4,404,344.

U.S. Pat. No. 4,530,914 discloses a catalyst system for thepolymerization of ethylene to polyethylene having a broad molecularweight distribution and especially a bimodal or multimodal molecularweight distribution. The catalyst system is comprised of at least twodifferent metallocenes and an alumoxane. The patent disclosesmetallocenes that may have a bridge between two cyclopentadienyl ringswith the bridge serving to make the rings stereorigid. The bridge isdisclosed as being a C₁ -C₄ alkylene radical, a dialkyl germanium orsilicon, or an alkyl phosphine or amine radical.

European Patent Application 0185918 discloses a stereorigid, chiralmetallocene catalyst for the polymerization of olefins. The bridgebetween the cyclopentadienyl groups is disclosed as being a linearhydrocarbon with 1-4 carbon atoms or a cyclical hydrocarbon with 3-6carbon atoms. The application discloses zirconium as the transitionmetal used in the catalyst, and linear or cyclic alumoxane is used as aco-catalyst. It is disclosed that the system produces a polymer productwith a high isotactic index.

It is known by those skilled in the art that polyolefins, andprincipally polypropylene, may be produced in various forms: isotactic,syndiotactic, atactic and isotactic stereoblock. Isotactic polypropylenecontains principally repeating units with identical configurations andonly a few erratic, brief inversions in the chain. Isotacticpolypropylene may be structurally represented as ##STR1## Isotacticpolypropylene is capable of forming a highly crystalline polymer withcrystalline melting points and other desirable physical properties thatare considerably different from the same polymer in an amorphous, ornoncrystalline, state.

A syndiotactic polymer contains principally units of alternatingconfigurations and is represented by the structure ##STR2## A polymerchain showing no regular order of repeating unit configurations is anatactic polymer. In commercial applications, a certain percentage ofatactic polymer is typically produced with the isotactic form. It ishighly desirable to control the atactic form at a relatively low level.

A polymer with recurring units of opposite configuration is an isotacticstereoblock polymer and is represented by ##STR3## This latter type, thestereoblock polymer, has been successfully produced with metallocenecatalysts as described in U.S. Pat. No. 4,522,982.

It may also be possible to produce true block copolymers of isotacticand atactic forms of polyolefins, especially polypropylene.

A system for the production of isotactic polypropylene using a titaniumor zirconium metallocene catalyst and an alumoxane cocatalyst isdescribed in "Mechanisms of Stereochemical Control in PropylenePolymerization with Soluble Group 4B Metallocene/MethyalumoxaneCatalysts," J. Am. Chem. Soc., Vol. 106, pp. 6355-64, 1984. The articleshows that chiral catalysts derived from the racemic enantiomers ofethylene-bridged indenyl derivatives form isotactic polypropylene by theconventional structure predicted by an enantiomorphic-sitestereochemical control model. The meso achiral form of theethylene-bridged titanium indenyl diastereomers and the meso achiralzirconocene derivatives, however, produce polypropylene with a purelyatactic structure.

Further studies on the effects of the structure of a metallocenecatalyst on the polymerization of olefins was reported in "CatalyticPolymerization of Olefins," Proceedings of the International Symposiumon Future Aspects of Olefin Polymerization, pp. 271-92, published byKodansha Ltd., Tokyo, Japan, 1986. In this article, the effects of thechiralities, steric requirements and basicities of ligands attached tosoluble titanium and zirconium metallocene catalysts on thepolymerization and copolymerization of propylene and ethylene werereviewed. The studies revealed that the polymerization rates andmolecular weights of the polymers obtained in the polymerization ofethylene with a zirconocene catalyst vary according to the basicity andsteric requirements of the cyclopentadienyl groups. The effects ofligands also contributed to the synthesis of polypropylenes with novelmicrostructures and high density polyethylenes with narrow and bimodalmolecular weight distributions.

The present invention relates to discoveries made as to varrying thebridge structure and substituents added to the cyclopentadienyl rings ina metallocene catalyst on the polymerization of propylene and highalpha-olefins. In particular, it was discovered that by varying thesecomponents, the physical properties of the polymer may be controlled.

SUMMARY OF THE INVENTION

As part of the present invention, it was further discovered that thenumber of inversions in the xylene insoluble fraction may be varied bychanging the components that form the bridge between thecyclopentadienyl rings in a metallocene catalyst. It was also discoveredthat the addition of various substituents on the cyclopentadienyl ringsalso varied the number of inversions. Thus, a means for varying themelting point of a polyolefin was discovered. This is a significantdiscovery, as heretofore it was the commercial practice to vary themelting points of polymer products by co-polymerizing varying amounts ofethylene to produce co-polymers with a range of differing meltingpoints. It is desirable to produce a homopolymer with varying meltingpoints without the use of ethylene. The present invention provides amethod for the production of homo-polymers with varying melting pointsby varying the structure of the metallocene catalyst used in thepolymerization.

Similarly, it was discovered-that by changing the structure of themetallocene catalyst, polymers are produced with varying molecularweights. Thus, the molecular weight of the polymer product may be variedby changing the catalyst. Accordingly, the present invention provides amethod for varying both the melting point and the molecular weight of apolymer product.

The present invention also provides a process for the polymerization ofolefins comprising contacting an organoaluminum compound with ametallocene described by the formula:

    R"(C.sub.5 R'.sub.m).sub.2 Me Q.sub.p

wherein (C₅ R'_(m)) is a cyclopentadienyl or substitutedcyclopentadienyl ring; R' is a hydrogen or a hydrocarbyl radical havingfrom 1-20 carbon atoms, each R' may be the same or different; R" forms abridge between the two (C₅ R'_(m)) rings and contains a bridge groupconsisting of an alkylene radical having 1-4 carbon atoms, a siliconhydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, an alkyl amine, a boron compound or an aluminum compound, andany of these bridge groups may contain any of these or other hydrocarbylgroups attached to the bridge; Q is a hydrocarbon radical such as analkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbonatoms or is a halogen; Me is a group 4b, 5b or 6b metal as positioned inthe Periodic Table of Elements; 0≦m≦4; and 0≦p≦3. An olefin monomer isadded to the metallocene catalyst and the organoaluminum compound. Afterthe polymerization has taken place, the polymer product is withdrawn.The process is characterized by the fact that it provides control of themelting point of the polymer product by controlling the number ofinversions in the xylene insoluble fraction of the polymer. The numberof inversions are effected by the R" group and the R' group. Thus, themelting point of the polymer product may be varied and controlled byvarying the R" bridge and/or the R' substituents on the cyclopentadienylrings.

The present invention also provides a method for varying the meltingpoints of polymer products and a method for varying the molecularweights of the polymer products. These methods include the use of themetallocene catalyst described by the above formula. The melting pointsand molecular weights of the polymer products are varied by changing theR" bridge and/or the R' substituents on the cyclopentadienyl rings.

DETAILED DESCRIPTION

The present invention provides a method of controlling the melting pointof a polymer by controlling the number of inversions in the chain of thexylene insoluble fraction of the polymers. The number of inversions arecontrolled in turn by the structure and composition of the catalyst, andthe number of inversions and hence the melting point of the polymerproduct may be controlled and varied by varying the catalyst. Inparticular, it has been discovered that varying the R" bridge betweenthe cyclopentadienyl rings will vary the melting point of the polymerproduct. Varying the R' substituents on the rings will also vary themelting point. In addition, it has been discovered that varying the R"bridge and/or the R' substitutents in the catalyst will also vary themolecular weights of the polymer products. These beneficial advantageswill become more apparent from the following detailed description of theinvention and the accompanying examples.

Normally, when propylene, or another alpha-olefin, is polymerized in acatalyst system prepared from a transition metal compound, the polymercomprises a mixture of amorphous atactic and crystalline xyleneinsoluble fractions which may be extracted using suitable solvents.Transition metal catalysts in the form of metallocenes have been knownfor some time, but up until just recently, such catalysts could onlyproduce predominantly atactic polymer which is not nearly as useful asthe isotactic form. It was discovered that by attaching a bridge betweenthe cyclopentadienyl rings in a metallocene catalyst and by adding oneor more substituents on the rings to make the compound both stereorigidand chiral, a high percentage of isotactic polymer could be produced. Asdescribed by the present invention, the composition of the bridge andthe substituents added to the rings affect the properties of the polymersuch as melting points and molecular weights.

The metallocene catalyst as used in the present invention must be chiraland stereorigid. Rigidity is achieved by an interannular bridge. Thecatalyst may be described by the formula:

    R"(C.sub.5 R'.sub.m).sub.2 Me Q.sub.p

wherein (C₅ R'_(m)) is a cyclopentadienyl or substitutedcyclopentadienyl ring; R' is a hydrogen or a hydrocarbyl radical havingfrom 1-20 carbon atoms, each R' may be the same or different; R" is thebridge between the two (C₅ R'_(m)) rings and is an alkylene radicalhaving 1-4 carbon atoms, a silicon hydrocarbyl radical, a germaniumhydrocarbyl radical, an alkyl phosphine, or an alkyl amine; Q is ahydrocarbon radical such as an alkyl, aryl, alkenyl, alkylaryl orarylalkyl radical having 1-20 carbon atoms or is a halogen; Me is agroup 4b, 5b or 6b metal as positioned in the Periodic Table ofElements; 0≦m≦4; and 0≦p≦3.

Exemplary hydrocarbyl radicals are methyl, ethyl, propyl, butyl, amyl,isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl, phenyl,and the like. Exemplary alkylene radicals are methylene, ethylene,propylene and the like. Exemplary halogen atoms include chlorine,bromine and iodine with chlorine being preferred.

The preferred transition metals are titanium, zirconium and hafnium. Qis preferably a halogen and p is preferably 2. R' is preferably a phenylor cyclohexyl group such that (C₅ R'_(m)) forms an indenyl radical whichmay be hydrated. As indicated, other hydrocarbon groups may be added tothe cyclopentadienyl rings. The preferred R" bridge components aremethylene (--CH₂ --), ethylene (--C₂ H₄ --), an alkyl silicon and acycloalkyl silicon such as cyclopropyl silicon, among others. Thepresent invention is such that the R" bridge and the R' substituents maybe varied among any of those compounds listed in the above formula so asto provide polymer products with different properties.

The metallocene catalysts just described are used in combination with anorganoaluminum compound. Preferably, the organoaluminum compound is analumoxane represented by the general formula (R--Al--O)n in the cyclicform and R(R--Al--O--)_(n) AlR₂ in the linear form. In the generalformula, R is an alkyl group with 1-5 carbons and n is an integer from 1to about 20. Most preferably, R is a methyl group. Generally, in thepreparation of alumoxanes from, for example, trimethyl aluminum andwater, a mixture of the linear and cyclic compounds are obtained.

The alumoxanes can be prepared in various ways. Preferably, they areprepared by contacting water with a solution of trialkyl aluminum, suchas, for example, trimethyl aluminum, in a suitable solvent such asbenzene. Most preferably, the alumoxane is prepared in the presence of ahydrated copper sulfate as described in U.S. Pat. No. 4,404,344 thedisclosure of which is hereby incorporated by reference. This methodcomprises treating a dilute solution of trimethyl aluminum in, forexample, toluene with copper sulfate represented by the general formulaCuSO₄.5H₂ O. The reaction is evidenced by the production of methane.

The metallocene catalysts used in the present invention are producedusing methods known to those skilled in the art. Typically, theprocedures simply comprise the addition of the MeQ groups describedabove and the R" group to a starting compound such as indene or someother substituted dicyclopentadiene.

The polymerization procedures useful in the present invention includeany procedures known in the art. An example of a preferred procedurewould be that disclosed in U.S. Pat. No. 4,767,735, issued Aug. 30,1988, hereby incorporated by reference which describes apre-polymerization of the catalyst before introducing the catalyst intoa polymerization reaction zone.

In the Examples given below, three different polymerization procedureswere utilized. These procedures, designated as A, B and C are describedas follows:

Procedure A

A dry two liter stainless steel Zipperclave was utilized as the reactionvessel and was purged with 2 psig of nitrogen. An alumoxane solution wasintroduced into the reaction vessel using a syringe which was followedby the introduction of the metallocene catalyst solution by a secondsyringe. Approximately, 1.2 liters of propylene are added at roomtemperature and then heated to the run temperature in 2-5 minutes wasthen added to the reaction vessel, and the agitator was set at 1200 rpm.The temperature of the reaction vessel was maintained at the runtemperature. After 1 hour of stirring, the agitator was stopped, thepropylene was vented, and 500 ml of either heptane or toluene was addedusing nitrogen pressure. The reactor was stirred for 5 minutes and thenthe contents were poured into a beaker containing 300 ml of a 50/50solution of methanol/4N HCl. After stirring for 30 minutes, the organiclayer was separated, washed 3 times with distilled water, and pouredinto an evaporating dish. After evaporating the solvent, the remainingpolymer was further dried in a vacuum oven.

Procedure B

The procedure is similar to Procedure A except that 1.0 liter ofpropylene was first added to the reactor. The alumoxane and catalystwere added to a 75 cc stainless steel sample cylinder and allowed toprecontact for several minutes before being flushed to the reactor with0.2 liters of propylene. The remaining procedures were as described inA.

Procedure C

Into a dry 500 cc stainless steel Zipperclave was added 120 cc of drytoluene and the temperature set at the designated run temperature. Thealumoxane solution was syringed into the reactor followed by theaddition of the catalyst solution by syringe. About 120 cc of propylenewas then added to the reactor using nitrogen pressure. After one hour ofagitation and temperature control, the agitator was stopped and thepropylene vented. The polymer was then extracted as described in A.

These are just examples of possible polymerization procedures as anyknown procedure may be used in practicing the present invention.

The polymer product may be analyzed in various ways for differingproperties. Particularly pertinent to the present invention are analysesfor melting points, molecular weights, and inversions in the chain.

The melting points in the examples below were derived from DSC(Differential Scanning Calorimetry) data as known in the art. Themelting points reflected in the tables are not true equilibrium meltingpoints but are DSC peak temperatures. With polypropylene it is notunusual to get an upper and a lower peak temperature, i.e., two peaks,and the data reflects the lower peak temperature. True equilibriummelting points obtained over a period of several hours would be 5°-12°C. higher than the DSC lower peak melting points. The melting points forpolypropylenes are determined by the crystallinity of the xyleneinsoluble fraction of the polymer. This is shown to be true by runningthe DSC melting points before and after removal of the xylene solublesor atactic form of the polymer. The results showed only a difference of1°-2° C. in the melting points after most of the atactic polymer wasremoved and isotactic polymer remained. The xylene insoluble fraction ofthe polymer yields a sharper and more distinct melting point peak.

NMR analysis was used to determine the exact microstructure of thepolymer including the mole fraction of inversions in the chain of thexylene insoluble fraction. The NMR data may be actually observed or itmay be calculated using statistical models. NMR analysis is used tomeasure the weight percent of atactic polymer and the number ofinversions in the xylene insoluble fraction of the polymer.

The molecular weights of the xylene insoluble fractions of the polymerswere calculated using GPC (Gel Permeation Chromatography) analysis. Forthe examples given below, the analysis was done on a Waters 150 Cinstrument with a column of Jordi gel and an ultra high molecular weightmixed bed. The solvent was trichlorobenzene and the operatingtemperature was 140° C. From GPC, M_(w), or the weight average molecularweight, and M_(n) are obtained. M_(w) divided by M_(n) is a measurementof the breadth of the molecular weight distribution.

As known in the art, the molecular weight of a polymer is proportionalto the rate of propagation of the polymer chain divided by the rate oftermination of the chain. A change in the ratio leads to a change in themolecular weights. As described by the present invention, a change inthe structure of the catalyst leads to a change in the ratio of therates of polymerization as well as a change in the melting points of thepolymer.

The following Examples illustrate the present invention and its variousadvantages in more detail. The Examples use various zirconocenes toillustrate the invention but similar results would be expected usingtitanocene, hafnocenes and other metallocene catalysts. The results aresummarized in Table 1.

EXAMPLE 1

The polymerization of propylene was carried out using 3 mg ofethylenebis(indenyl)zirconium dichloride as the catalyst and usingpolymerization Procedure B as outlined above. Enough alumoxane was usedto produce a Al/Zr metal atom ratio of 1.4 mol Al/mmol of Zr. Thereaction temperature was 30° C. The polymerization produced a yield of51.0 grams of polypropylene which results in an efficiency of 17.0 kg ofpolypropylene/g of catalyst in 1 hour (kg/g.cat.1 h). Atactic polymerwas removed by dissolving the polymer product in hot xylene, cooling thesolution to 0° C., and precipitating out the isotactic form. Theintrinsic viscosity of the xylene insoluble fraction was calculated tobe 0.495 dl/gm from measurements taken on a Differential Viscometer indecalin at 135° C. The GPC analysis showed a M_(w) of 40,000 and a M_(w)/M_(n) of 2.2 for the xylene insoluble or xylene insoluble fraction. Theresults are summarized in Table 1.

EXAMPLE 2

Polymerization Procedure C as described above was used with 2.00 mg ofethylenebis(indenyl)zirconium dichloride as the catalyst. The Al/Zrratio was 2.1 (mol/mmol) and the reaction temperature was 50° C. Inaddition to the analyses performed in Example 1, DSC analysis for a peaktemperature or melting point (T_(m)) of the xylene insoluble fractionand analysis of the NMR spectrum for the mole fraction of inversions inthe isotaction fraction in the chain were performed. The results areshown in Table 1.

EXAMPLE 3

Polymerization Procedure A as described above was used with 0.6 mg ofethylenebis(indenyl)zirconium dichloride as the catalyst. The Al/Zrratio was 7.0 (mol/mmol) and the reaction temperature was 50° C. Theresults of the polymerization and analysis are shown in Table 1.

EXAMPLE 4

The procedures of Example 3 were repeated except that 1.43 mg ofcatalyst were used, the Al/Zr ratio was 2.9 (mol/mmol) and the reactiontemperature was 80° C. A tremendous increase in the yield and efficiencyof the catalyst were obtained. The results are shown in Table 1.

EXAMPLES 5-8

In these Examples, the catalyst used wasethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, thetetrahydrated form of the catalyst used in Examples 1-4. This was donein order to demonstrate the effect of a different substituent on thecyclopentadienyl rings. The polymerization runs were carried out usingvarying procedures, catalyst amounts, Al/Zr ratios, and temperatures asindicated in Table 1. The results in Table 1 show a different range ofmelting points (T_(m)) and molecular weights (M_(w)) as the catalyst washydrogenated.

EXAMPLES 9-11

These Examples used a zirconocene catalyst with a dimethyl siliconbridge instead of an ethylene bridge. The catalyst used wasdimethylsilylbis(indenyl)zirconium dichloride. The polymerizationconditions and results are shown in Table 1. With the substitution of asilicon bridge for an ethylene bridge, the melting points and molecularweights increased.

EXAMPLES 12-17

These Examples used a catalyst with a cyclopropyl group attached to asilicon bridge--thus the catalyst wascyclopropylsilylbis(indenyl)zirconium dichloride. The polymerizationconditions and results are shown in Table 1. Slightly higher meltingpoints and molecular weights were obtained with this structure ofcatalyst.

EXAMPLE 18

In this example, a zirconocene catalyst with a larger bridge structurewas used; the catalyst used was1,1,4,4,-tetramethyl-disilylethylenebis(indenyl)zirconium dichloride inthe amount of 1.45 mg. The Al/Zr ratio was 6.0 mol/mmol and the reactiontemperature was 50° C. The reaction was run for an hour, but nosignificant amount of polypropylene was formed. In other tests, thiscatalyst was shown useful in the polymerization of ethylene and acopolymer of ethylene and propylene.

                                      TABLE 1                                     __________________________________________________________________________                                         Mole Percent                                                                  of Inversions                                 Poly.   Al/Zr                                                                              Temp.                                                                             Yield                                                                            Efficiency                                                                           Tm °C.                                                                      in Isotactic                                                                        I.V.                               Example                                                                            Proc.                                                                            Cat. mg.                                                                           mol/mmol                                                                           °C.                                                                        gms                                                                              kg/g · cat · 1                                                     DSC Peak                                                                           Fraction                                                                            dl/gm                                                                            Mw/1000                                                                            Mw/Mn                      __________________________________________________________________________    1    B  3.0  1.4  30  51.0                                                                             17.0   140        0.50                                                                             40   2.2                        2    C  2.0  2.1  50  20.0                                                                             12.7   135.2                                                                              2.5   0.23                               3    A  0.6  7.0  50  25.4                                                                             33.3   135.3      0.33                                                                             23   2.2                        4    A  1.43 2.9  80  221.0                                                                            154.5  125.6                                                                              4.5   0.23                                                                             14   2.1                        5    A  19.6 0.2  20  16.5                                                                             0.8    143.0                                                                              1.2   0.39                               6    B  49.9 0.1  10  13.0                                                                             0.3    139.7      0.42                                                                             29   3.5                        7    A  1.86 2.3  50  33.0                                                                             17.7   136.8      0.18                                                                             11   2.3                        8    A  3.38 1.3  80  265.0                                                                            78.4   120.9      0.10                               9    A  3.5  1.3  30  8.7                                                                              2.5    145.2      0.61                                                                             50   2.2                        10   C  2.0  2.2  50  64.0                                                                             32.0   142.3                                                                              1.6   0.46                                                                             36   2.3                        11   A  0.7  6.4  80  20.5                                                                             29.3   135.3                                                                              3.1   0.27                                                                             18   2.2                        12   B  10.0 0.5  30  1.8                                                                              0.2    146.7      0.41                               13   B  1.0  4.6  30  6.0                                                                              6.0               0.55                               14   B  3.1  1.5  50  1.8                                                                              0.6    141.5      0.40                                                                             30   3.4                        15   B  1.0  4.6  50  14.0                                                                             14.0              0.48                               16   A  2.89 1.6  80  5.8                                                                              2.0    138.2      0.36                                                                             26   2.7                        17   B  2.50 1.8  80  69.0                                                                             27.6              0.41                               18   B  1.45 6.0  50  0  0                                                    __________________________________________________________________________

The results shown in Table 1 illustrate some of the advantages of thepresent invention. The substituents on the cyclopentadienyl rings andthe compositions and structures of the bridge between the rings do havea significant influence on the stereoregularities, melting points andthe molecular weights of the polymers. These effects are a result of thesteric and electronic properties of the substituents and bridgestructures.

It is noted that the polymerization temperature is a factor in theformation of the polymer product. At the lower reaction temperatures,the melting points and molecular weights for the same catalyst werehigher. As the reaction temperatures increased, the melting points andthe molecular weights decreased. Also, as the reaction temperatureincreased, the yields and catalyst efficiencies also increased, usuallydramatically.

Some of the advantages of the present invention are realized bycomparing the polymer properties of Examples using different catalystsbut run at the same polymerization temperature. In making thesecomparisons, it can be seen that the melting points increased and themole fraction of inversions decreased as the R" bridge structure waschanged from ethylene to an alkyl silicon bridge. The molecular weightsalso increased as silicon was substituted for ethylene. The results showthat polymers with lower molecular weights are produced by catalystswith more bulky and more basic ligands. Also, some increase was noted asthe indenyl groups were hydrated. Thus, the more electron dontaing thatthe R' and R" groups are, the molecular weights of the products can beexpected to be higher. The results clearly show that the melting pointsand molecular weights can be varied by changing the bridge structure andthe substituent groups in the cyclopentadienyl rings.

Example 18 illustrates a limit to the number of atoms forming the R"bridge. Apparently, the steric effect of inserting two carbon atoms andtwo alkyl silicon groups was too great and caused the catalyst to shiftin such a way as to block the production of propylene.

It is known that the mole fraction of inversions in the isotacticpolymer chain does correlate with the melting points. When the molefractions are plotted against the log T_(m), the points fit a straightline through the regions tested in the Examples. The equation for theline is mole fraction of inversions=-0.5 log T_(m) (°C)+1.094. As thenumber of inversions increase, the melting point of the polymerdecreases. The number of inversions also vary as the R" bridge ischanged.

Having described a few embodiments of the present invention, it will beunderstood by those skilled in the art that modifications and adoptionsmay be made without departing from the scope of the present invention.

I claim:
 1. A catalyst system for polymerization of propylene havingincreased molecular weight and melting point comprising(a) a chiral,stereorigid metallocene catalyst described by the formula:

    R"(C.sub.5 R'.sub.m).sub.2 Me Q.sub.p

wherein (C₅ R'_(m)) is a cyclopentadienyl or substitutedcyclopentadienyl; R' is hydrogen or hydrocarbyl radical having from 1-20carbon atoms, each R' may be the same or different; R" is a siliconhydrocarbyl radical and acts as an interannular bridge between the two(C₅ R'_(m)) rings; Q is a hydrocarbon radical chosen from the groupconsisting of an aryl, alkyl, alkenyl, alkylaryl and arylalkyl radicalhaving 1-20 carbon atoms or is a halogen; Me is a group 4b, 5b, or 6bmetal as designated in the Periodic Table of Elements; 0≦m≦4; and 0≦p<3;and (b) an organoaluminum compound.
 2. A catalyst system as in claim 1wherein the organoaluminum compound is alumoxane represented by theformula:

    (R--Al--O).sub.n

or

    R(R--Al--O).sub.n AlR.sub.2

wherein R is an alkyl group with 1-5 carbons and n is an integer from 1to
 20. 3. A catalyst system as in claim 1 wherein Me is titanium,zirconium or hafnium.
 4. A catalyst system as in claim 3 wherein Me iszirconium.
 5. A catalyst system as in claim 1 wherein R" is an alkylsilyl or cycloalkyl silyl radical.
 6. A catalyst system as in claim 5wherein R" is dimethyl silicon.
 7. A catalyst system as in claim 5wherein R" is cyclopropyl silicon.
 8. A catalyst system as in claim 1wherein C_(p) R'_(m) is indenyl.
 9. A catalyst system as in claim 1wherein Q is a halogen and _(p) is
 2. 10. A catalyst system as in claim1 wherein the metallocene catalyst isdimethylsilylbis-(indenyl)zirconium dichloride.
 11. A catalyst system asin claim 1 wherein the metallocene catalyst iscyclopropylsilylbis-(indenyl)zirconium dichloride.
 12. A catalyst systemas in claim 9 wherein Q is chlorine.